I do realize that this is an old thread.
However, I also have a PRO-94 and the manual I have which I downloaded in PDF format states exactly what is stated in this thread.
Manual reads....
USING THE AUTO BACKLIGHT DISPLAY
You can set the scanner so the auto backlight turns on
for about 5 seconds when the scanner receives signals.
If you press a key (except the LIGHT BUTTON) within 5 seconds, the
display remains lighted for more than 15 seconds.
To turn auto backlight display on or off, turn off the scanner.
Then hold down LIGHT BUTTON and turn on the scanner. "on
Aut Lit" briefly appears when auto backlight is on. "OFF
Aut Lit" briefly appears when auto backlight is off.
I know that there are three versions of the PRO-94 and mine is the first version as it is not an A or B version.
I am wondering if this backlight display feature is only available on the later versions as my PRO-94 does not work when attempting this backlight feature.